Conventionally, video display devices which are used to observe video images while mounted on the head have been referred to as head mounted displays. For example, the displays disclosed in Japanese Patent Application Kokai No. H8-320453 and Japanese Patent Application Kokai No. H7-284041 are known as examples of such displays. In the head mounted displays disclosed in these patents, a holding part that holds a display part has a so-called hair band shape, and the display part is held in front of the eyes by mounting this holding part on the forehead.
However, in the case of such conventional head mounted displays, when the display is mounted on the head, the holding part that holds the display part is positioned laterally along the forehead; accordingly, the following problem arises: namely, the display is relatively unsightly. Furthermore, especially in the case of women, the problem of cosmetics and the like adhering to the holding part also arises.
In most cases, such a video display device is constructed so that this device is mounted on the head in a form that is wrapped around the head; such display devices include a binocular type in which a video display system is formed in positions corresponding to both eyes, and a monocular type in which a video display system is formed in a position corresponding to only one eye, i.e., either the left eye or right eye. Of these two types, the binocular type is used mainly for the enjoyment of videos. In the case of monocular type displays, for example, use as display devices or the like in wearable personal computers, or as display devices that display instructions to workers, is expected.
Furthermore, although use as display devices or the like in wearable personal computers, or use as display devices that display instructions to workers, is expected in the case of display devices of the monocular type, switching of the display screen and the like, and operating members such as operating buttons that operate the image display, are required in both cases.
In such head mounted displays, numerous operating members such as buttons are ordinarily attached to a controller that is used to operate the display device and the like, and the display is operated by an action such as the pressing of these operating members. However, in the case of a head mounted display, since video images are displayed with the line of sight of the user blocked, it is difficult for the user to ascertain where the buttons or the like are located in the controller.
In Japanese Patent Application Kokai No. H11-174991, a method is described in which this problem is solved by disposing the buttons on different surfaces making up the controller, so that visual confirmation of the positions of the buttons is unnecessary. In this case, however, it is not possible to install a very large number of buttons; furthermore, the buttons are installed on a controller that is separate from the main body of the head mounted display. Accordingly, the controller and the display main body must be connected by a cable or the like.
Furthermore, in Japanese Patent Application Kokai No. H11-136598, the operating switch of a head mounted display that projects video images onto both eyes is attached to the main body of this head mounted display. However, in the case of a monocular head mounted display, since the eye onto which the video images are projected may be switched, it is necessary to construct the operating switch so that the feeling of operation does not vary greatly as a result of such switching. Moreover, especially in the case of a head mounted display of the type in which the eye that is used is switched by mounting the display with the up/down and left/right directions reversed at the time of mounting, it is desirable that the relative positions of the operating members not vary even when the up/down and left/right directions are reversed; furthermore, it is desirable to devise the display so that this relative positional relationship is reflected in the display device.
Furthermore, in the case of monocular type head mounted displays, the outside scene can be viewed with the eye that is not viewing video images; accordingly, such head mounted displays offer the following advantage: namely, such displays are relatively safe compared to binocular type head mounted displays. On the other hand, since different images are seen by both eyes, there is a problem in that concentration on the video image is impossible; furthermore, there are problems of eye fatigue and the like due to visual field competition.
As one countermeasure against this, a head mounted display which has a member that blocks light to the eye that is not observing video images has been disclosed in Japanese Patent Application Kokai No. H4-341078.
However, in the case of the head mounted display described in Japanese Patent Application Kokai No. H4-341078, since the light blocking member constantly covers one eye, safety problems occur in the same manner as in a binocular type head mounted display.
Furthermore, in the optical design inside the display part of a conventional head mounted display, since it is a prerequisite that the eye of the observer be disposed in a predetermined position (eye point), the observer can observe images in a favorable manner by utilizing the mounting fittings to align the eye and the eye point.
However, during actual use, the eye of the observer is not necessarily disposed at the eye point. For example, an observer using eyeglasses must place the lenses of the eyeglasses between an eye and the display part; accordingly, the position of an eye is inevitably before the eye point. Furthermore, in cases where the observer moves or the like while wearing the head mounted display, an eye may be intentionally shifted from the eye point, so that the observer observes the images of the head mounted display while viewing the outside world. In cases where the display is thus used with an eye shifted from the eye point, a loss of the peripheral portions of the images is unavoidable.
Furthermore, in cases where the display device is devised so that the display part can be displaced between a protruding state and a retracted state, the user must perform an operation that causes the image output part to protrude each time that the user uses the display. Furthermore, following the completion of use, the user must perform an operation that retracts the image output part. Accordingly, a problem is predicted whereby the display will be bothersome to use.
Furthermore, when the user utilizes the head mounted display device, various utilization scenarios may be envisioned, such as outdoor use and desk work. The distance from the ordinary user to the object of observation naturally differs for each of these utilization scenarios. For example, this distance is approximately 50 cm in the case of desk work, several meters in the case of use in an electric train, and infinity in the case of outdoor applications. Utilization in which the head mounted display switches between the outside scene and video images inside the device is also conceivable; in such cases, however, the user must observe while adjusting the focus between the outside scene and the video images, so that the user easily becomes fatigued. Furthermore, the manner of feeling also varies among individuals. In addition, there are differences between the left and right in individuals.